Addressing the Design-to-Test Challenges Bob Cutler and Greg Jue, Agilent Technologies
Software Defined Radios Flexibility Radio can support multiple waveforms: Different formats, Different revisions of a format, Backwards compatibility, Future-proofing Combination of DSP/FPGA/GPP C++/HDL Flexibility increases demands on RF HW performance HW may be flexible or reconfigurable to more efficiently support waveforms with significantly different characteristics (e.g. OFDM vs MSK) Portability Across single vendors platforms (usually proprietary) Across multiple vendors platforms (based on standards such as SCA) Portability of waveform components (e.g. Viterbi decoder)
Portability and Flexibility Challenges and Opportunities RF performance determined by both hardware and software. Performance could change with bug fix. HW platforms may come from different vendors and have different capabilities. Not quite write-once, run anywhere. Probe points in the signal path are now digital, as well as analog. Need a consistent way to measure. Component implementations in C++, HDL, possibly also from different vendors. Need to design and test hardware to support waveforms that have yet to be invented. Can use test waveforms for development, diagnostics and manufacturing test.
SDR Designs: Comprised of Baseband AND RF Bits In Coding Algorithms D/A Tx Channel Rx A/D Decoding Algorithms Bits Out Gain Linearity Output Power Gain NF Phase Noise SDR Design: RF Transmitter: Upconverts Signal to RF RF Receiver: Downconverts Received RF Signal to IF or IQ Coding/Decoding Algorithms to Achieve System Performance
Baseband Waveforms Come in Many Formats- Creates Barriers for SDR RF Design & Test Bits In Coding Algorithms D/A Tx Channel Rx A/D Decoding Algorithms Bits Out Simulation Models FPGA HDL Code Math Algorithms SDR Transmitter: Baseband waveforms needed to design & test RF: Challenge: How can RF designs be designed & tested with various baseband waveform sources? SDR Receiver: Baseband coding/decoding needed to design & test RF receivers for coded BER metrics Challenge: How can Receiver BER performance be evaluated independently of baseband waveform HW? Baseband Hardware
Agilent SystemVue Integrated Design Environment to Bring FPGA and RF Designs Together Baseband and RF modeling, simulation Open, model-based design infrastructure for continuous verification of heterogeneous IP Math/C++ /GUI Fixed Pt VHDL/Verilog HDL generation & co-simulation IP reference blocksets for Mobile WiMAX, LTE, other formats Customizable, standards-based test vectors Interoperable with Agilent test equipment Test equipment links, VSA integration, and more Mobile WiMAX is a registered trademark of the WiMAX Forum
Design SDR RF Using Various Types of Waveform Formats Use Waveform Sources to Design SDR RF Waveform Sources HDL Code FPGA Hardware Simulation Models Algorithm Code Waveform Signal Source Simulated RF Transmitter Design
Example 1: Use HDL-Based WiMAX Waveform to Design SDR RF Transmitter Simulated SDR Transmitter Output Waveform Sources HDL Code FPGA Hardware Simulation Models Algorithm Code EVM = 8.4% Simulated RF Transmitter Design VSA Measurement
Example 2a: Use FPGA-Based Legacy Waveform to Design SDR RF Transmitter Simulated SDR Transmitter Output Waveform Sources HDL Code FPGA Hardware Simulation Models Algorithm Code EVM = 9.1% Simulated RF Transmitter Design VSA Measurement
Example 2b: Re-Configure FPGA-Based Waveform to Evaluate SDR RF Transmitter Design Interoperability Simulated SDR Transmitter Output Waveform Sources HDL Code FPGA Hardware Simulation Models Algorithm Code Reconfigure legacy FPGA waveform for a new waveform (LTE) EVM=10.5% Simulated RF Transmitter Design VSA Measurement
Example 2c: Probing an FPGA Waveform with Dynamic Probe Waveform Sources HDL Code FPGA Hardware Simulation Models Algorithm Code Simulated RF Transmitter Design preliminary work-in-progress
Example 3a: Use Simulation-Based WiMAX Waveform to Design SDR RF Receiver Waveform Sources HDL Code FPGA Hardware Simulation Models Algorithm Code Waveform Simulation Source Waveform Simulation Receiver Simulated RF Receiver Design Pre-Configured Algorithm Models (Customizable) Select ADC model
Example 3a Results: WiMAX BER vs. ADC Jitter QPSK BER vs. ADC Jitter vs. EbNo 16 QAM BER vs. ADC Jitter vs. EbNo 64 QAM BER vs. ADC Jitter vs. EbNo Red: 4% ADC Jitter Blue: 6% ADC Jitter Green: 8% ADC Jitter
Example 3b: Replace Waveform to Evaluate SDR Receiver Design Interoperability New BER Results New Waveform Simulation Source Replace WiMAX Waveform Source & Receiver with LTE New Waveform Simulation Receiver Simulated RF Receiver Design
Example 4: Use Algorithm Code Waveforms Waveform Sources HDL Code FPGA Hardware Simulation Models Algorithm Code Customize OFDMA Algorithms
SDR Hardware Testing SDR Testing Challenges: Custom/proprietary waveforms not supported by COTS test equipment Flexible SDR test platforms are needed for today s and tomorrow s waveforms Different tools used between design and test- makes it difficult to debug issues Solution- Combine the flexibility of simulation with test equipment for flexible SDR testing
Adding Flexibility to SDR Testing with Simulation Test waveform coding/decoding SW-defined Customizable algorithms Customizable test waveforms 14 Bit A/D Board DUT 16822A Logic Analyzer with Agilent SystemVue* * Note: SystemVue does not ship with Logic Analyzer
OFDMA BER Hardware Test Results
Design-to-Test Tool Consistency Helps Minimize Unwanted Surprises and Helps to Debug Issues Simulation Code Generation RF FGPA/DSP D/A Digital Signal Capture Analog Baseband
Simulate an SDR Receiver with a Hardware Front End (N6841 RF Sensor) Wideband RF Sensor Simulated RF Receiver Design Simulated SDR Receiver Output VSA Measurement HW DUT Test Signal
Cognitive Radio Many definitions of CR. A radio that is aware of its environment and adjusts its behavior accordingly. Key application for CR is Dynamic Spectrum Access (DSA) Radio adjusts frequency, power, modulation based on sensed spectrum, location, policy and databases Complimentary to SDR in this application
Filling the Whitespace Goal: Increase spectrum utilization without causing interference
CR Design and Measurement Considerations Interference (actual, or potential for) Radio System Performance (capacity, link establishment and reliability) Radio Physical Layer Performance (e.g. adjacent channel power) Environment Sensing Performance (spectrum sensing, location sensing) Policy Performance (does the policy over, or under protect) Radio Environment (channel, noise, occupancy)
Radio Environment In many applications, such as TVWS, very little is actually known about real environments Where are the wireless microphones and TV signals? What are their power statistics? What other signals are present? Are they protected? How dynamic are they? How does all of this change from one location to another? For joint spectral detection, what does the environment look like from two or more locations at any one instant in time? Need to design for real environments Need to capture and replicate environment in the lab
Challenges of Spectrum Sensing From this display can you tell me 1. Is the spectrum occupied? 2. How occupied is it? 3. What is the potential for interference? 4. What signals are present?
Challenges of Spectrum Sensing (cont) Performance of various spectrum sensing algorithms False positives, False negatives Response to real-world signal environment (dynamic, many signals) Radio Design Spurious Amplitude accuracy Intermod distortion Sensitivity Selectivity Frequency accuracy Speed/complexity/Cost tradeoffs
Summary: CR Development Challenges Need to characterize, capture, and replicate real-world spectral environments. Needs to be done over time, frequency and location. Need to capture the environment as signals, not power spectra Need to use captured environments to evaluate CR algorithms and radio link performance. Need to evaluate performance using non-ideal radios. Need a flexible and comprehensive CR R&D Testbed!
Cognitive Radio R&D Testbed
CR Algorithm Development & Testing Environment
Mobile WiMAX Case Study
Step 1: Capture Signal & Bring into SystemVue Captured CR environment
Step 2: Whitespace Math Algorithms Determine Valid Whitespace Frequency Rules Policy Valid whitespace determined within the policy Rising/falling edges detected to determine whitespace RF Sensors
Debugging Whitespace Algorithms Single-Step Through Code Add/Remove Breakpoint Code Variable Values are Displayed as Code is Single-Stepped
Step 3: Whitespace Math Algorithms Determine Valid Whitespace WiMAX spectrum (scaled and centered in the valid whitespace)
Analyze Detect-And-Avoid Interferer Scenarios Narrowband Interferer Sweep Narrowband Interferer vs. Frequency to Evaluate Impact on OFDMA BER
Step 4: Identify Detected Signals in Simulation or with Test Equipment Sensed spectrum
Video Demo with SystemVue + N6841A N6841A is Remotely Located Across Washington State Remotely Located N6841A RF Sensor www.agilent.com/find/eesof-cognitive-whitepaper
New Whitepaper Available: www.agilent.com/find/eesof-cognitive-whitepaper
Summary Use waveforms sources in various formats (HDL, FPGA hardware, simulation models, math algorithms) to design SDR transmitters and receiver and evaluate interoperability Customizable simulation waveforms (WiMAX and LTE) Seamless integration between design and test capability creates flexible SDR testing platform enables R&D engineers to develop and test algorithms and hardware with real field signals Evaluate Cognitive Radio link performance, perform what-if detect-and-avoid interference scenarios Explore a Cognitive Radio simulation example in the SystemVue 2009.08 example set request a free evaluation at: www.agilent.com/find/eesof-systemvue-latest-downloads Or, contact your local Agilent representative
Additional Resources Product Websites: http://www.agilent.com/find/systemvue http://www.agilent.com/find/rfsensor Whitepapers & Application Notes: Videos: Cognitive Radio Algorithm Development and Testing: http://www.agilent.com/find/eesof-cognitive-whitepaper Software Defined Radio Measurement Solutions: http://cp.literature.agilent.com/litweb/pdf/5990-4146en.pdf Solutions for Addressing SDR Design and Measurement Challenges http://www.agilent.com/find/sdr http://www.agilent.com/find/powerofx Web video of CR Testbed discussed in this webcast: http://www.agilent.com/find/eesof-cognitive-whitepaper
Q&A
Thank You!